Little evidence for entropy and energy excess beyond r500 - An end to ICM preheating?

Abstract

Abstract Non-gravitational feedback affects the nature of the intra-cluster medium (ICM). X-ray cooling of the ICM and in situ energy feedback from AGN’s and SNe as well as preheating of the gas at epochs preceding the formation of clusters are proposed mechanisms for such feedback. While cooling and AGN feedbacks are dominant in cluster cores, the signatures of a preheated ICM are expected to be present even at large radii. To estimate the degree of preheating, with minimum confusion from AGN feedback/cooling, we study the excess entropy and non-gravitational energy profiles upto r200 for a sample of 17 galaxy clusters using joint data sets of Planck SZ pressure and ROSAT/PSPC gas density profiles. The canonical value of preheating entropy floor of ≳ 300 keV cm2, needed in order to match cluster scalings, is ruled out at ≈3σ. We also show that the feedback energy of 1 keV/particle is ruled out at 5.2σ beyond r500. Our analysis takes both non-thermal pressure and clumping into account which can be important in outer regions. Our results based on the direct probe of the ICM in the outermost regions do not support any significant preheating.